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Lipids
Iva Klimešová
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Like carbohydrate, a lipid molecule is composed of
carbon, oxygen, and hydrogen atoms linked together
in a specific and unique way.
There are three different functions for lipids in
our bodies:
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Energy source
Energy storage
Forming the membranes around our cells.
Providing the starting material (cholesterol) for making
hormones
Carrying the fat-soluble vitamins (A, D, E and K) and
carotenoids)
The largest amount of energy is stored in the body as
fat.
Lipids contain a lot of calories in a small space.
• Fats are stored as triglycerides in both the
muscle tissue and adipose (fat) tissue.
• Essentially, a lipid molecule consists of one
glycerol molecule and three fatty acid molecules
to form triglyceride.
• Fatty acids have two unique characteristics:
1. the length of their carbon chain (Food contain fatty
acids with chain length of 4 to 24 carbons.)
2. the bonding of carbon atoms
The length of carbon chain:
• Short-chain fatty acids (SFA) have 4 to 8
carbons; sources: milk and dairy produce
(SFA are the major end products of bacterial metabolism in the human
large intestine.)
• Medium-chain fatty acids (MFA) have 9-12
carbons; sources: milk and dairy produce,
coconut and palm oil
• Long-chain fatty acids (LFA) have more than
12 carbon; source: many animal fats
• The shorter the carbon chain, the more liquid the fatty
acid becomes (the lower its melting point). Oils are
usually of the short-variety.
• Shorter fatty acids are more water-soluble, a property
that affects their absorption in the digestive tract.
The bonds of carbon chain
• saturated fatty acids with only single
bonds linking carbons together
H
H
H
H OH
R - C glycerol
H
C - C - C - C= O
H
H
H
• unsaturated fatty acids with at least one
double bonds in the carbon chain
– Monounsaturated
(a fatty acid in which the carbon chain contains
one double bond)
– Polyunsaturated
(a fatty acid in which the carbon chain contains
two or more double bonds)
H
H
H
H
H
H
OH
R - C = C - C - C = C - C - C= O
glycerol
H
H
• There are different types of fatty acids in
one molecule of triglyceride.
• Regardless of the degree saturation, all
lipid have essentially the same number of
calories per unit weight.
The American Heart Association has set guidelines for
triglyceride levels in blood:
Level mg/dL Level mmol/L Interpretation
<150
<1.69
Normal range, lowest risk of CVD
150-199
1.70-2.25
Borderline high
200-498
2.25-5.63
High level, high risk of CVD
>500
>5.65
Very high, increased risk of CVD
Saturated fats
• At room temperature, saturated fats are usually solid.
• Source: primarily in animal products including beef,
lamb, pork and chicken, egg yolk, dairy fats of cream,
milk, cheese, butter; coconut and palm oil; non-dairy
creams because they contain coconut oil
• Consumption of saturated fats has been linked with risk
of coronary heart disease:
– sources of saturated fat are full of cholesterol (except coconut
and palm oil)
– diet high in saturated fat facilitates cholesterol synthesis by
the liver (including coconut and palm oil)
Unsaturated fats
• At room temperature, unsaturated fats are usually liquid.
• Monosaturated
• Sources: olive, peanut, canola, rape oil, almonds, avocado
• Polyunsaturated
• Sources: sunflower, soybean, corn, and safflower oil, fish
oil, walnuts, sesame seeds, pumpkin seeds, tofu, lard
• Unsaturated fatty acids are sensitive to heat and light
damage – store them in the dark bottles and use for cold or
short hot preparations
• Humans and other mammals can synthesize saturated and some
monounsaturated fatty acids from carbon groups in carbohydrate and
protein.
• Polyunsaturated fatty acids an omega-3 fatty acid and an omega-6 fatty
acid are considered essential fatty acids (because they cannot be
synthesized by humans).
Essential fatty acids:
• omega-3
The parent fatty acid of the omega-3 series is alpha-linolenic acid (ALA) (ALA
contains 18 carbon atoms and 3 carbon-carbon double bonds, 18:3).
ALA- humans can synthesize eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA) from ALA
Sources: flaxseed oil, soybean oil and canola oil, nuts, seafish – salmon,
herring, sardine, tuna
• omega-6
The parent fatty acid of the omega-6 series is linoleic acid (LA) (LA contains 18
carbon atoms and 2 carbon-carbon double bonds, 18:2).
LA - humans can synthesize dihomo-gamma-linolenic acid (DGLA) and
arachidonic acid (AA) from LA
Sources: olive and sunflower oils, sesame, pecans, pine nuts, freshwater fish –
carp, trout, catfish, eel
• Clinical signs of essential fatty acid deficiency decreased
growth in infants and children, increased susceptibility to
infection and poor wound healing.
• Omega-6 and omega-3 PUFA are important structural
components of cell membranes, they are important to central
nervous system function, and they play important roles in
vision.
• Typical Western diets tend to be much higher in omega-6
fatty acids than omega-3 fatty acids.
• It has been estimated that the ratio of omega-6 to omega-3
fatty acids in the diet of early humans was 1:1, but the ratio in
the typical Western diet is now almost 10:1 due to increased
use of vegetable oils rich in LA and declining fish
consumption.
• Omega-3 intakes are associated with significant reductions in
cardiovascular disease risk, the American Heart Association
recommend that all adults should eat fish, particularly oily
fish, at least twice weekly.
• A large body of scientific research suggests that
increasing the relative abundance of dietary
omega-3 fatty acids may have a number of
health benefits.
• Increasing EPA and DHA intake may be
beneficial to individuals with diabetes,
especially those with elevated serum
triglycerides.
Approximate percentage of fatty acids in common fats and oils
canola oil (rapeseed)
olive oil
soybean oil
sunflower oil
pork fat (lard)
butterfat
palm oil
coconut oil
0
20
40
polyunsaturated
60
monosaturated
80
saturated
100
Cis Versus Trans
• Otherwise identical unsaturated fatty acids can
have different shapes.
• The carbon chain of a cis fatty acid is bent, and
the chain of a trans fatty acid is straighter.
• Most naturaly occuring unsaturated FA are cis FA.
Trans-unsaturated fatty acids (TFA)
• TFA are product of hydrogenation which increases the
saturation of fatty acids within oils and converts natural cis
to trans configuration
• Hydrogenation= industrial process that chemically
transforms a low melting point oil into a solid fat with a
higher melting point to enhance product taste, stability and
shelf life.
• Found in commercially fried foods (French fries, popcorn),
commercial baked goods and snacks (cakes, cookies,
biscuits), margarine, and cheap vegetable shortenings
(not in e.g. Flora, Rama).
• Trans-fatty acids have many adverse metabolic effects
including elevation of LDL („bad“) cholesterol,
triglycerides, reduction in HDL („good“) cholesterol,
and adverse effects on endothelial function,
inflammatory markers, and probably insulin resistance.
• The diet in northern European countries has traditionally contained
more trans-fatty acids than the diet in Mediterranean countries in which
olive oil is commonly used.
• Mean daily intakes of trans-fatty acids in European countries range
from minimal values in Italy, Portugal, Greece and Spain to greater
values for Germany, Finland, Denmark, Sweden, France, United
Kingdom, Belgium, Norway, the Netherlands, and Iceland.
• Recent decreases in the trans content of the diet have been observed,
presumably due to modifications of commercially available fats or
changes in consumer choices.
• Today, most margarines in the European market have a lower content
of trans fatty acids than 5 to 10 years ago and in most cases the
change has been carried out without adverse effects for the consumer.
• The technologies used here are now implemented in
a number of other industries. New technologies have been
adopted to solve specific problems in, for example,
the bakery and chocolate confectionery.
Cholesterol
• Cholesterol is non-fat substance vital to human
metabolism, and although it may be obtained in the
diet only from animal foods, the body can produce
its own way.
• The recommended cholesterol intake is less then
300 milligrams per day (the richest source is egg
yolk has 220 mg).
• A positive relationship has been established
between high blood cholesterol levels and coronary
heart disease, reduction of dietary cholesterol has
been advocated by a number of health
recommendations.
• Fruits, vegetables, grains, and nuts have no
cholesterol.
Cholesterol content – egg and meat
group
Amount Cholesterol (mg]
Eggs
1
220
Liver, kidney, brains 1 oz
120
Shrimp
1 oz
45
Beef, pork, ham
1 oz
25
Poultry
1 oz
23
Fish
1 oz
21
Cholesterol content – milk group
Amount
Cholesterol (mg]
Ice cream
1 cup
85
Milk, whole
1 cup
27
Milk, 2%
1 cup
15
Milk, skim
1 cup
7
Cream cheese
1 tbsp
18
Butter
1 tbsp
12
Type of Fat
Dietary Sources
Total
Cholesterol
LDLHDLcholesterol cholesterol
Triglycerides
Saturated Fat
Red meat, cheese, butter,
commercially fried foods
and baked goods
Increase
Increase
No effect
No effect
Trans Fats
Commercially fried foods
and commercially prepared
snacks and baked goods
Increase
Increase
Slight
Decrease
No effect
Monounsaturated Nuts, olives, avocados, olive
Decrease
Fats
& canola oils
Decrease
No effect
No effect
Polyunsaturated
Fats
: Omega-6
Corn, soybean and
safflower margarine & oils
Decrease
Decrease
Decrease
Unknown
Omega-3
Salmon, mackerel, herring,
Decrease
flaxseed, walnuts, walnut
oil, soybean and soybean oil
Decrease
No effect
Decrease
•Recommendation is that total daily fat intake be limited to < 30% of total
daily energy intake
•with no more than 10% provided by saturated and trans fats,
•polyunsaturated fatty acids should be limited to no more than 10% of total
daily energy intake (Because polyunsaturated fatty acids may also lower HDLcholesterol as well as LDL-cholesterol)
•10% provided by monounsaturated fats
Digestion and absorption
• Digestion of fats starts in the stomach by the action of linqual
lipase, an enzyme secreted in the mouth. This enzyme
digests short- and medium-chain saturated fatty acids.
• The stomach secretes gastric lipase which works with
linqual lipase to digest a very small amount of fat.
• The major breakdown of lipid occurs in the small
intestine.
• The fat is emulsified into very small droplets by the action of
bile (secreted from gallbladder) - it facilitates enzyme action.
• Pancreatic lipase, the main fat-digesting enzyme, degrades
some of the triglyceride molecules to monoglycerides and fatty
acids.
• In this simpler form, monoglycerides are more easily
absorbed by the intestine.
• The absorbed glycerol, fatty acid, and monoglyceride
molecules are then free to recombine to reform triglycerides.
• The fatty acids take one of two routes
depending on their chain length:
– Short- and medium-chain fatty acids
proceed to the portal vein and empty into the
liver.
– Long-chain fatty acids and cholesterol is
first reconverted to a chylomicron and then
transported through the lymphatic system into
the systemic vein that empty into the heart.